1. Field of the Invention
The present invention is related to a method used in a wireless communication system, and more particularly, to a method of handling a link failure in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of a universal mobile telecommunications system (UMTS), for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmission/reception, uplink multiple-input multiple-output (UL-MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
The UE may receive packets (e.g., transport blocks (TBs)) transmitted by two eNBs, when the UE is configured with a dual connectivity. Throughput of the UE is improved when the dual connectivity is operated. However, wireless links between the UE and the eNBs may not be stable due to characteristics of the wireless links. For example, a radio link failure may happen between the UE and one of the eNBs. The UE does not know how to report the radio link failure when the dual connectivity is realized by the UE and the eNBs. In another example, the UE may fail to complete a random access procedure with one of the eNBs. Similarly, the UE does not know how to process the failure of the random access procedure. In another example, the UE may fail to transmit a radio link control (RLC) packet data unit (PDU) to one of the eNBs, e.g., when the maximum number of retransmissions is reached. Communications between the UE and the eNBs may not be proceeded regularly, if the retransmission of the RLC PDU cannot be solved.
Thus, how to solve the abovementioned failures of the operations is an important topic to be discussed.